Pfizer’s proposed merger with AstraZeneca, which has so far been resisted by the would-be British bride, has some Democratic members of Congress and the White House up in arms. They claim that so-called inversion deals, in which U.S. corporations buy companies based in more tax-friendly jurisdictions, like the U.K., Ireland, and Switzerland, are chiefly motivated by tax avoidance. As part of the deals, the U.S. firms move their legal domicile to the acquired company’s country.

An outraged Sen. Carl Levin (D., Mich.) plans to introduce legislation this week to raise the bar on deals that result in a brand new corporation chartered in these lower-tax locales. He introduced a similar bill during President Obama’s first term. “A loophole in our tax laws allowing these inversions threatens to devastate federal tax receipts. We have to close that loophole,” Levin said. The bristle is that the managements often keep managing the new company from the U.S. …

… Tax differences affect a company’s economic output. So it’s logical for a global company to relocate from the comparatively toxic U.S. to a lower-tax country. The U.K. has about a 20% corporate tax rate, versus as high as 35% in the U.S. The U.K. also has a lower rate for revenue derived from intellectual property, which is a special attraction to science-based companies like pharmaceuticals. The U.K. also has a territorial tax system that does not tax corporate income earned abroad. The U.S. taxes income from wherever when it is returned home, minus the taxes paid overseas. Thus, there is over $2 trillion of cash held outside the U.S. by U.S. companies.

Comprehensive reform won’t happen until either Hillary Clinton or the GOP’s to-be-announced candidate occupies the Oval Office. Pfizer (ticker: PFE) has no reason to wait. Estimated tax savings from the $100 billion deal are $1 billion a year.